What is Intranet

Every body knows What is Internet. I heard the word intranet long ago. But i didn't think seriously about that. But now i was thinking about a subject to post to my lot suddently this came to my mind. Can anybody expain to me What is intranet.

A network based on TCP/IP protocols (an internet) belonging to an organization, usually a corporation, accessible only by the organization's members, employees, or others with authorization. An intranet's Web sites look and act just like any other Web sites, but the firewall surrounding an intranet fends off unauthorized access.
Like the Internet itself, intranets are used to share information. Secure intranets are now the fastest-growing segment of the Internet because they are much less expensive to build and manage than private networks based on proprietary protocols.

An intranet is a private computer network that uses Internet protocols, network connectivity, and possibly the public telecommunication system to securely share part of an organization's information or operations with its employees. Sometimes the term refers only to the most visible service, the internal website. The same concepts and technologies of the Internet such as clients and servers running on the Internet protocol suite are used to build an intranet. HTTP and other Internet protocols are commonly used as well, especially FTP and e-mail. There is often an attempt to use Internet technologies to provide new interfaces with corporate 'legacy' data and information systems.
Briefly, an intranet can be understood as "a private version of the Internet," or as a version of the internet confined to an organization.